Children’s behavior at age 3 offers some surprising clues about their risk of developing addictive behaviors like problem gambling or drug misuse in their 30s, according to data from an ongoing study of nearly 1,000 people in New Zealand.

The research, which has so far tracked participants’ psychological, economic and intellectual life course from birth to age 32, involves virtually all of the children born in Dunedin, New Zealand, between April 1972 and March 1973.

The new analysis, which was published in Psychological Science, found that children whose temperament was deemed “undercontrolled” at age three were more than twice as likely as well-adjusted kids to have problems with gambling at age 21 and 32. About 10% of the children exhibited this type of temperament at that age, which involves a lack of self control, including rapidly shifting emotions, impulsive and willful behavior and relatively high levels of negative feelings.

The association held true even after controlling for factors like IQ, gender and socioeconomic status. And when these children were assessed as adults, they still rated high on feelings of alienation and continued to express high levels of negative emotion. They also tended to be less conscientious and less socially agreeable than their peers.

Long-term studies like the Dunedin project are critical for sussing out the roots of addiction. A key question that has long plagued addiction researchers is: Do factors like problem drug-taking or gambling lead to impulsive behavior — and depression — or are people who start out feeling low and acting impulsively more vulnerable to getting hooked?

“This can help to tease apart chicken-and-egg-type questions — that is, which came first,” says Wendy Slutske, professor of psychological science at the University of Missouri and the lead author of the study. “In this case, we have firmly established that undercontrolled temperament comes before any involvement in gambling. This is an important piece of the puzzle in developing a theory of the development of problem gambling.”

Howard Shaffer, director of the division on addiction at Harvard Medical School, who specializes in problem gambling and was not associated with the study, described the study as an “important contribution to the field.”

“There are few longitudinal studies,” Shaffer says, “and, in addition to providing a longitudinal study, this research extends the opportunity to examine predictors downward to a very young age. This research also is important because it begins to clarify the nature of the many important non-gambling variables that contribute to excessive and disordered gambling.”

Researchers aren’t yet sure why the undercontrolled temperament is linked with addictive behavior. Some people with this temperament may enjoy gambling because it allows them to escape from their elevated levels of negative emotions; others may simply be at higher risk because of their reduced impulse control. Both factors combined would be riskiest of all.

Slutske notes some additional explanations: “One possibility is that there are genetic factors that are related to both low self-control and gambling or problem gambling. Another possibility is that children who are low in emotional and behavioral control tend to associate with other undercontrolled children who introduce them to gambling activities.”

Once an individual develops a gambling habit, Slutske says, their low emotional and behavioral control may lead to worse decision-making while gambling, or losing control during a gambling session, which may in turn lead to gambling problems.

Gambling isn’t the only addiction risk associated with the undercontrolled temperament. An earlier analysis of the Dunedin population found that children with the most undercontrolled behavior at ages 3 and 5 had more than three times the risk of becoming addicted to multiple drugs as young adults, compared with those who had exhibited the highest levels of self-control.

The findings underline the idea that some people are innately more vulnerable to addictions than others — not because they seek extra pleasure, but because they have a pre-existing excess of negative emotions and an inability to control them.

The research also highlights an often-overlooked truth about addiction: it is not simply the result of exposure to an addictive substance. “This study reminds us that exposure to gambling is insufficient to explain the emergence of gambling disorders. Disordered gambling requires a relationship between gambling and gamblers who have certain characteristics,” says Shaffer. “This is not to say that some people absent these traits might not become disordered gamblers or that all people with these characteristics will become disordered gamblers, but there is an important association beginning to emerge from longitudinal research.”

Indeed, an earlier longitudinal study in California suggested the same kinds of associations, finding that preschool children who had less impulse control and higher levels of emotional distress were more likely to develop drug problems later. Interestingly, in that study, the healthiest preschoolers were not the ones who ended up abstaining from all drug use — in fact, abstainers showed high anxiety and poor social skills from the start. Instead, the youth who had the best behavior as preschoolers turned out to use marijuana moderately in adolescence, but did not have difficulty controlling their use.

The New Zealand and California studies add to the increasing scientific evidence that addiction is not the result only of drug use or experience with activities like gambling, but rather that the minority of people who do become addicted overwhelmingly have pre-existing problems. At least half of addicted people have another mental illness, such as depression or an anxiety disorder, and these data suggest that those conditions or the temperaments that predispose people to them are key contributors to the addiction.

This means that treatment for gambling or substance problems cannot focus solely on the addictive behavior. “Clinicians must address the full spectrum of issues that tend to cluster with disordered gambling. It is not enough to focus exclusively on gambling activities. Key player attributes will need attention as well,” says Shaffer.

Slutske cautions, however, that it is by no means inevitable that undercontrolled children will develop gambling problems or addictions. “Although it is remarkable that one can predict whether one will develop a gambling problem in adulthood from a 90-minute observational assessment at age 3, it is also important to understand that an undercontrolled 3-year-old is not doomed to become an adult problem gambler,” she says. “They are just at increased risk. This means that there were many undercontrolled children — in fact, the majority — who did not have any gambling problems as adults.”

Nonetheless, another implication of the research is that targeting self-control — rather than particular substances or activities — might also be an important part of prevention. Interestingly, many undercontrolled children “outgrew” their self-control problems over time, and learned to rein in their impulses as well as their peers who showed earlier mastery.

“I think an important observation about self-control is that it is much less stable than other traits, such as intelligence,” says study co-author Avshalom Caspi, professor of neuroscience at Duke University. Noting that a correlation cannot be larger than 1.0 — which in this case refers to a factor in childhood being the same in adulthood 100% of the time — Caspi explains that the stability of IQ from childhood to adulthood is around 0.8, while the stability of personality traits like self-control is far lower, at 0.3.

“This tells us that over the course of life, there is quite a bit of change in self-control, and perhaps that potential for change can be harnessed more deliberately by people,” he says.